This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Tgo protein can form heterodimers with other PAS domain partners and function as important transcriptional regulators in Drosophila midline development. EMSA shows that Tgo-bHLH-PAS can form homodimers that bind to a specific DNA sequence as well. However, the Tgo-PAS monomer is much more stable than the homodimer, as determined by gel filtration. It is possible that self association of the bipartite PAS domain prevents dimerization between two Tgo-PAS molecules.